1. Field of the Invention
The invention relates to medical instrumentation, and more particularly it relates to devices for plasma-arc cutting of biological tissues.
2. Description of the Prior Art
It is possible to use for cutting biological tissues various devices wherein either an indirect arc or a microplasma arc is formed.
There is known a plasma-arc cutting device including a housing accommodating therein a cathode assembly and an anode assembly. The anode assembly includes a nozzle of a complicated shape, receiving an electrode having its pointed end facing the direction of forming an electric arc. The cathode assembly has channels for feeding a plasma-forming gas (Advertising Manual "Elektrodugovyie plazmotrony", Novosibirsk, 1980, pp. 34-35).
Devices of this kind are unsuitable for cutting biological tissues, as their microplasma jet is of a power inadequate for maintaining a required speed of cutting biological tissues; furthermore, they are rated for operation with a relatively high working pressure of the plasma-forming gas, which results in excessive saturation of biological tissues with the gas. The temperature of the plasma jet produced by this known device is within 5000.degree. C., which is insufficient for cutting biological tissues and causes heat lesions of the biological tissues at the side of the cut to a considerable depth.
There is further known a device for plasma-arc cutting of biological tissues, likewise comprising a cathode assembly and an anode assembly. The electrode of the cathode assembly has a tapering portion having its pointed end facing the area of generation of the electric arc. The cathode assembly has passages formed therein for supplying the plasma-forming gas. The anode assembly has a nozzle receiving the tapering portion of the electrode, the nozzle successively defining a cylindrical chamber, a tapering chamber, an arcing chamber and a plasma arc forming chamber, in the quoted order (SU, A No. 275261, Beresnev A. S. et al., 1970, Bulletin No. 22).
In this device, however, the arcing process in the arcing chamber is insufficiently stable at low flow rates and pressure of the plasma-forming gas, which shortcoming should be eliminated to make the device suitable for applications in medicine. Moreover, under these conditions the anode spot eventually moves from the arcing chamber into the tapering chamber of the nozzle, which results in the dropping voltage at the arc and its diminishing power, impairing the cutting and coagulating properties of the plasma jet. To restore the anode spot into the arcing chamber, it is necessary to step up the working pressure of the plasma-forming gas, e.g. to 2.times.10.sup.5 Pa, and then to reduce it once again to the working feed pressure of 1.times.10.sup.5 Pa. However, this periodic increasing of the working pressure of the gas results in an increasing velocity of the issuing plasma jet, complicating the surgeon's task and threatening injuries to organs not being operated upon.